Acoustic tile and method of manufacturing the same



.YI/1 July 10 1934- A M. H. KLIOTH 1,966,069

- AcousTIc TILE AND METHOD oF MANUFACTURING Tan sm:

Filed oct. 2s. 1932 melggygwsoa PLASUC Cf OSS Reference Ea BY I l, m,'75"' Cross Reference the like. y i gran character.

Patented July 10, 1934 .UNITED STATES PATENT oFFica ACOUSTIC TILE ANDMETHOD 0F MANUFACTURING THE SAME Max H. Kliefoth, Madison, Wis.,assigner to C. F.

Burgess Laboratories, Delaware Application October 26.

' z5 claims.

5 acoustic tile which combines a high coemcient of sound absorptiontogether with structural rigidity so that it may he used without anysupporting facing material when applied as by means of an adhesive towalls, ceilings and other surfaces.

10' It is a further object to make, by new methods,

such a tile of ceramic or other non-combustible materials having a typeof surface which is decorative and pleasing to the eye. i

Although many types of acoustical tiles and especially ceramic and othernon-combustible types of acoustical tiles have been and are being made,these tiles have not been entirely satisfactory. Such tiles either aretoo fragile, or when sufllciently strong have too low a coeillcient ofabsorption. Many also are not decorative and are not capable of beingdecorated.

'I'he acoustic tiles which I have invented, and which are the subjectmatter of this application, are formed rst by shaping a mixture o i'particles of a body material and a wet adhesive comprising sodiumsilicate. The shaped tiles are then dried. 'I'he intercommunicatingpores or channels necessary to give such dried tiles the necessaryproperty of absorbing sound are not formed by using a deficiency ofadhesive in the wet mixture to `leave iriterstices or openings betweenthe body particles but are formed by the shrinkage of the adhesive andother moist materials'during the operations which remove moisture fromthe wet shaped tile. It is due largely to this method of producing theporosity that I attribute the excellent qualities of the tile that I amable to produce by the methods which are to be hereinafter described. Itis understood that the specic examples to be given and the proportionsof the materials used are merely illustrative and the invention asexpressed by the claims is not limited thereto.

The body material which may be used may be fibrous in character such asa mineral wool which s ool, glassv wool, slag wool. asbestos ma eria aso may e Intermediate forms of body material may be used. The granularmaterial may either be of organic or inorganic nature. It is preferablynon-combustible. G anular coq erably non-metallic, may either beanatural Inc., a corporation of 1932, serial No. 639,597

it may be an artificial or'ceramic material such as baked and vitriedclay products. It also may r na ural granular be a spec a 1y ma e aproduct or it may be a specially shaped product,

as, for example, the hollow beads or tubes de- 50 scribed in mycopending application Serial No. 625,558, filed July 28, 1932. Itusually is desirable to have the absorbing tile as light in weight aspossible and therefore a porous or other light weight aggregate orgranular material such as pumice stone, blown granular slag andwaterfioated slag is desirable and preferable.

The alkali silicate may be potassium silicate but it preferably issodium silicate because of its lower cost. SiOz to NazO ranging from2.85 to 1 and 3.25 to 1 are preferred but silicates of other ratios maybe used. Mixtures of these may be used.

Method for making a fibrous tile Amixing it with the water. To 5 partsof this shredded news stoclggin suspension in 250 parts of water isadded 5 parts by weight of a 42 B. solution of 3.25 to 1 so llicate.Shortbered asbestos may replace a portion of the wood ber to decreasethe shrinkage during drying. After a homogeneous suspension is obtaineda s of the cleaned mineral wool in a mixing container and thoroughlystirred. Too much working of the fragile mineral wool must be avoided orits fibrous character is destroyed. The mixture is thickened by drainingoff the excess water. This operation coats and stiifens (after drying)the individual fibers of mineral wool with a thin envelope of a gel ofprecipitated sodium silicate which probably is a silica gel. The wood orpaper bers in the gel reenforce the structure. This stiiening envelopemay be omitted if desired but for best results it should be used.

Sodium silicates having a ratio of 7 55 product such as hed rock ofvarious kinds together are then added to and mixed with this 110signeren-rter thickened slurry. A 47 B. 2.85 to 1 ratio sodium silicatepreferably is used. This mixture is shaped into a tile and'dried. Themixture is shaped by brush tamping it into a mmm-.w

. sible to remove a much larger percentage of water chemicals act whenboth suction and pressure are used without decreasing the size of theinterstices produced by the removal of the water. The apparent densityof the tile is thereby not increased as compared to the increase inapparent density when a similar amount of water is removed from the tileby compression alone. The evaporation costs for drying the tile also aredecreased thereby. ABecause of the light pressure used this methodproduces a `moist pad in which interstices of the required size remainbetween the bers of mineral wool. The water previously in theseinterstices is largely removed in this first step. The removal of theexcess water leaves moist alkali silicate to cement the fibers togetherand produces a moist pad which is light in weight and may be easilyhandled as' compared to the heavy soggy mass, which is tender anddiilicult to handle should excess water remain in the interstices.

The tile is then dried in a drier such as an oven or it may be driedbetween steam platens. he`

dryinmtsnharatet nce of the silicate resul mxgra. n g` li silicofiuoridereferably eaii silica e sincoiluoride decreases greatly the migration ofthe silicate to the surface of the tile during drying to strengthen thestructure greatly. It also increases appreciably its water resistanceafter drying. The anti-migrating agent is incorporated with the alkalisilicate just prior to its addition to the slurry of mineral wool sothat appreciable gelling of the silicate is avoided. About 16 parts ofsodium silicofluoride added to the 200 parts of sodium silicate givesexcellent results. From 12 to 20 parts may be used. It is preferablyadded to the silicate in powder form. Smaller amounts are not effectiveenough and larger amounts gel the silicate sumciently to interfere withits adhesive properties. A high speed mixer may be used for thispurpose. With this proportion of silicouoride, the tiles may be dried atabout 300 F. without appreciable intumescence of the silicate. A tile 1%inches thick dries in about 7 hours at 300 F. l

When the above procedure vis followed th shrinkage of the tile duringdrying is very small, usually being about 5% or less'. This smallshrinkage helps to produce a high porosity. 'me

creased s l urther by incorpora uv z cate so that the borax may be usedwithout the silicouoride. The waterproofing of alkali silicates by meansof borax is the subject matter of my copending application Serial No.574,457 filed November 1l, 1931.

The tile may be made more resilient and flexible by incorporating asmall amount, 4 to 10 parts, of latex with 200 parts of sodium silicateadhesive, as described and claimed in my copending application SerialNo. 652,696, filed January 20, 1933. It is preferably incorporated incon junction with the alkali silicoiluoride to keep it highly dispersedthroughout the alkali silicate as described and claimed in -rnycopending application Serial No. 652,695, led January 20, 1933. Theproperties of the alkali silicate may be modifled further by theaddition of small amounts of gums and like materials. i

During the drying operation a small amount of adhesive draws to thesurfaces of the tile forming rather dense top and bottom surfaces. Oneof these dense surfaces is removed as by sanding to expose the poroussound absorbing interior structure. This sanded surface is exposed tothe sound when the tile is mounted. The other dense surface ispreferably not removed so that the breathing of the tile (passage of airthrough the tile) is cut to a minimum.

The tile made as described consists of mineral wool fibers thinly coatedand stiiiened with a thin hardened precipitated sodium silicate or gelreenforced with pulp fibers, though these may be omitted if desired.These stiffened fibers are knitted together by the binder comprisingdriedy removing or drying operations to form the neces' saryintercommunicating interstices and pores to give the desired soundabsorption.

In the ordinary process of making an acoustic tile in which theparticles of aggregate are thinly coated with viscous alkali silicateand then formed into a tile and dried, the silicate dries to a thinglossy coating on each particle. The binder or coating thus formed whenviewed under the microscope appears to be smooth and continuous.However, the silicate binder of this invention formed by the methodhereinbefore described when examined under the microscope has anentirely different appearance. VIt appears to consist of smalldiscontinuous areas of alkali silicate on each particle, the crevicesbetween adjacent areas usually extending to the surface of the particlewhich is coated. The areas are often jagged in appearance. The tryingprocess appears to be analogous to the drying of mud whereby shrinkagecracks are formed.

The resulting tile is stiff and suiilciently hard so that it may behandled with but ordinary care without danger ,of breaking. It may beglued to ,surfaces without danger of splitting under itsnecissaxywiwlueffoi acostical @106. COMPosmoNs,

comme R PLAsuc muposesl, If the amount of adhesive is decreased, as bythinning out the alkali silicate with water, so as to prevent theformation of a solid block, the resulting pad is flimsy and possesseslittle strength.

The alkali silicate alone, when heated in the drying operation,especially in commotion with the wick action of the mineral wool, hasthe property of migrating to the hot surfaces and forming a hardimpervious crust, and thereby leave the interior practically free ofadhesive. The interior portion is therefore without any strength. Aspreviously described, this migration or flowing of the alkali silicatewhen heated may be prevented by incorporating an anti-migrating orsetting agent.

A ller, which preferably is of smal article sisu t fi'. .magma teadhesive.

tilF l d @www usegnlelnovi cess water previous o rying. As an exanl 1 eswimgh sound absorbing coeicient, made according to the above describedmethods, may have a weight of about 26 lbs. per cu. ft. and may haveabout of voids.

One type of a combined suction and pressure box or mold for forming thetile is shown diagrammatically in Fig. 1. It consists of a perforated orporous bottom plate 10 on which the wet slurry 1l is thrown. The sides12 of the box retain the slurry and form the sides of the mold. 'I'hehopper bottom 13 of the box has a pipe connection 14 to a vacuum pump(not shown) which is used to maintain a suction on bottom plate 10 forremoving the excess water from slurry 11. A drain 15 allows the water tobe removed from the hopper bottom 13. A plate or plunger 16 ts withinthe sides 12 of the mold and is used to apply light pressure to thetop-of the slurry 11. It is actuated by means of arm and leverarrangement 17. Stops 18 are provided to regulate the thickness of thewet, formed tile.

Experience teaches how much slurry must be introduced into the meold andhow much pressure to apply to the slurrfor making a tile ofpredetermined density and stiffness, the stiffness or rigidity dependingin part on the density. If the light pressure alone is applied to themoist slurry the resultant shaped wet tile has a high water content. Ahigh pressure reduces the water content but it also increases thedensity of the-tile by decreasing the size of the interstices betweenthe bers. By applying suction with light pressure the water content isgreatly reduced compared to that of a tile produced by pressure alone.'I'his greatly reduces the drying time and costs. Furthermore the wettile is much more easily hand led when the water content is reduced.

It is obvious to those skilled in the art that with a slight change inthe apparatus the presure may be applied with air instead of by theplate 16. It is also possible to make use of a continuous machine bydepositing the slurry on a traveling Cross Reference Method for makinggranular aggregate tile The body material for the granular aggregatetile which is stone-like in appearance and feel and which may .be usedas a facing for the mineral wool tile previously described, ispreferably a iht-weight aggregate such as'pumice-stone. This 1s gr mdto'w'ithin the desired screen sizes depending upon the desired porosityand other characteristics of the tile. An aggregatepassing througlra 20mesh screen and retained qnmagmmesh screea-is-excellent for absorbingtiles used`u1'der ordinary conditions. 1f

aggregates may be made as will be apparent to those skilled in the art.

To the above pumice stone aggregate a moist adhesive comprising analkali silicate is added and thoroughly mixed therewith. F 65 parts byweight of the pumice'stonegouh partspf a viscois' sodium\siiicate'ma'ybe used. A 2.85 SiOrrl/Naz ratiodium silicate of 47 B. is suitablerthough"silicates of other ratios may be used. This amount ofsilicateshould ll substantiallyallofint'erstices between the aggregszieparticles. I preferrhowever,to add `to the -silicatemirtsofan-a't'i-migrating "agent such as sodiunsiliconuoride whichminimizes the migration of.silicate tothe surface of the tile whenheated while being dried. As previously noted, this silicoiluoride alsominimizes the in.

4of' the marble us With-orwthout 3 parts of kieselguhradddtth'e'abovemots'f aggregate-an7silicate giveexcellentaesults. It maybe necessary to add an additional 2 or 3 parts of water with thesefiller additions. Ii necessary to further increase the Water resistanceof the silicate 2 parts of borax may be added.

A small amount of latex, 1 to 3 parts, may be added to the silicateespecially in the presence of the silicofluoride, to thereby increasethe resilience and flexibility of the tile. Gums and like materials alsomay be incorporated with the alkali silicate in small amounts to furthermodify its properties.

The wet mixture of materials is pressed into a suitable form to shapethe tile. The wet tiles are then dried in an oven or between steamheated plates. If an anti-migrating agent is used in the mixture atemperature of 300 F. is suitable and substantially no intumescenceoccurs. Without this agent the temperature used must .be much lower soas to dry the sllicate without intumescence. The tile is kept under heatunil dry. The adhesive shrinks because of the removal of the waterduring the drying operation so that the intercommunicatng intersticesbetween the aggregate particles are again opened up, the adhesiveshrinking onto and coating the aggregatel rkgnly one of the surfaces isground oi,th otheraimse backingsurface which prevents breathing of thetile. vA paper or sheet asbestos backing may be baked onto the tileduring the manufacturing Examiner operations so as to make an imperviousback.

Throughout the specification and claims the term mineral wool is used inthe generic sense and includes various types of non-metallic, in-

organic, fibrous materials, both natural and artineral, such as @www l,min' eral wool, etc. The properties o these var woo er what and themanufacturing procedure and proportions of ingredients must be variedsomewhat with the different raw materials.

It also is possible to vary the proportions of ingredients'from thosegiven for the same type of mineral wool. As an example the sodiumsilicate may be a 421/2 B. 3.25 SiOzzl NazO ratio solution instead ofthe 47 B. 2.85 SiOzzl NazO ratio solution. 'lhepameuntrrpusedmglbeLalidmount Of I e2.: '1 um: agent maybe varied. Son o he l eralwv'oolsand teristics vary. The acoustical properties of such a compositeabsorber may be more easily controlled by making it of two or morelayers, each layer having pores or interstices of different sizes sothat each of such layers has its own acoustical properties which differto some extent from those of the other layers. One layer may have abrous body material and the other may have a granular body material. Thethickness of each layer with respect to the other layer or layers isdetermined by the acoustical properties desired for the composite nishedabsorber. The composite absorber preferably is built up while the bodymaterials are in the wet state after which the composite wet absorber issubjected to the dewatering or drying operations previously.described.The variation in the size of the interstices of the strata is mosteasily obtained by changes in the particle sizes and shapes of the bodymaterial.

If the composite absorber referred to above is composed of layers, oneof which has a fibrous body material and the other of which has agranular body material, it usually is desirable to make the granularmaterial the exposed facing because of its advantageous properties forthat purpose. The base of fibrous body material, if made in accordancewith mv improved method as hereinbefore described, is strong enough tosupport such a facing without disintegrating or pulling apart under theconditions of use. Such a composite tile may be made by making thefibrous base and granular facing separately and then gluing themtogether but it is made preferably by facing the brous base with thegranular facing before drying, the two being formed from theirrespective wet mixes into a unitary structure, and then drying thecombined wet layers to form the combination tile. Care must be takenwhen making such composite tile that the channels or pores in both thebase and facing are continuous from one into the'other.v

I claim: 1. An acoustic absorber comprising particles of a body materialand an alkali silicate binder and containing a multiplicity ofintercommunicating pores or channels therethrough formed by theshrinkage of said binder by the drying thereof said dried bindercomprising a dried alkali silicate characterized by a multiplicity ofdiscontinuous small areas thereof and by a. multiplicity of shrinkagecracks.

2. The acoustic absorber of claim 1 in which the silicate binder has ananti-migrating agent incorporated therewith.

3. The acoustic absorber of claim 1 in which the silicate bindercomprises the reaction product of sodium silicate and an alkalisilicouoride.

4. The acoustic absorber of claim 1 in which the body material isfire-resisting and in which the silicate binder comprises the reactionproduct of sodium silicate, sodium silicouoride and borax.

5. 'I'he method of making an acoustic absorber comprising' particles ofa bocLv material and a binder and containing a multiplicity ofintercommunicating pores or channels therethrough, which comprisesmixing particles of a body material with a wet adhesive comprisingalkali silicate in an amount that substantially fills the intersticesbetween said particles of body material; said adhesive being of suchcomposition that on drying it shrinks sufiiciently to leave amultiplicity. of intercommunicating ypores or channels between saidparticles shaping said mixture, and removing water from said shapedmixture until dry substantially without intumescence of said silicate toshrink wet constituents of said shaped mixture to form saidintercommunicating pores or channels.

6. Ihe method of making an acoustic absorber comprising particles of abody material and a binder and containing a multiplicity ofintercommunicating pores or channels therethrough, whichcomprises mixingan anti-migrating agent with a wet adhesive comprising alkali silicate,and mixing particles of a body material with an amount of said wetadhesive that substantially lls the interstices between said particlesof body material, said adhesive being of such composition that on dryingit shrinks sufficiently to leave a multiplicity of intercommunicatingpores or channels between said particles shaping said mixture, andremoving water from said shaped mixture until dry substantially withoutintumescence of said silicate to shrink wet constituents of said shapedmixture to form said intercommunicating pores or channels.

'7. An acoustic tile comprising sized particles of a non-combustibleaggregate and an alkali silicate binder and containing a multiplicity ofintercommunicating pores or channels therethrough formed by theshrinkage of said binder by the drying thereof, said dried bindercomprising a dried alkali silicate characterizedby a `multiplicity ofdiscontinuous small areas thereof and by a multiplicity of shrinkagecracks.

8. 'I'he acoustic tile of claim 7 in which the non-combustible aggregateis porous and in which the silicate binder comprises the mixture of afiller with the reaction product of an alkali silicate and awater-proongagent.

9. The acoustic tile of claim 'I in which the aggregate is pumice stoneand in which the silicate binder comprises the reaction product ofsodium silicate and sodium silicoiiuoride.

10. An acoustic absorber comprising fibrous material and an alkalisilicate binder and containing a multiplicity of intercommunicatingpores or channels therethrough formed by the shrinkage of said .binderby the drying thereof, 150

I Nl

106. COMPOSITIONS, COATING 0R PLASTlC said dried binder beingdistributed throughout said brous material and enveloping individual:bers thereof and comprising aI dried alkali silicate, 4characterized bya multiplicity of discontinuous small areas thereof and by amultiplicity of shrinkage cracks.

11. Ihe acoustic absorber of claim 10 in which the fibrous material ismineral wool and in which the alkali silicate has an anti-migratingagent incorporated therewith.

12. An acoustic tile comprising mineral wool and an alkali silicatebinder and containing a multiplicityof intercommunicating pores orchannels therethrough formed by the shrinkage of said binder by thedrying thereof, the bers of said mineral wool having a stitfeningenvelope comprising dried gelled alkali silicate, said dried alkalisilicate binder being characterized by a multiplicity of discontinuoussmall areas thereof andby a multiplicity 'of shrinkage cracks.

13.' The acoustic tile of claim 12 in which the gelled alkali silicatestiiening envelope for the mineral wool ilbers contains paper pulp andin which the binder comprises the reaction product of sodium silicateand alkali silicofiuoride.

14. The acoustic tile of claim 12 in which the gelled alkali silicatestiiening envelope for the mineral wool bers contains a reinforcingagent and in which the binder comprises alkali silicate having ananti-migrating agent incorporated therewith.

l5. 'I'he acoustic tile of claim 12 in which the gelled alkali silicatestiflening envelope for the mineral wool iibers contains paper pulp andin which the binder comprises alkali silicate having an anti-migratingagent incorporated therewith.

16. An acoustic tile comprising a base of fibrous material and an alkalisilicate binder and an aldherent facing on said base comprising sizedparticles of an aggregate and a silicate binder, both base and facingcontaining a multiplicity of intercommunicating pores or channelstherethrough formed by the shrinkage of said binder by the dryingthereof, said dried binder being distributed throughout said fibrousmaterial and enveloping individual bers thereof, said binder for boththe .base and facing comprising a dried alkali silicate characterized bya multiplicity of discontinuous small areas thereof and by amultiplicity of shrinkage cracks. l Y

17. The method of making an acoustic absorber comprising a brousmaterial and ab'inder and containing a multiplicity ofintercommunicating pores or channels therethrough which comprises mixingan anti-migrating agent with an alkali silicate to form an adhesive,mixing said brous material with said wet adhesive to form a thickslurry, said adhesive being of such composition that on drying itshrinks sumciently to leave a multiplicity of intercommunicating poresor channels between bers of said fibrous material shaping said slurry,and removing water from said shaped mixture until dry substantiallywithout intumescence of said silicate to shrink said wet constituents ofsaid shaped slurry to form said intercommunicating pores or channels.

18. The method of making an acoustic tile comprising a mineral wool anda binder and containing a multiplicity oi intercommunicating Vpores orchannels therethrough which comprises mixing an alkali silicofluoridewith sodium silicate to form a wet adhesive, mixing said mineral woolwith said wet adhesive to form a thick slurry, said adhesive being ofsuch composition that on drying it shrinks suiciently to leave amultiplicity of intercommunicating pores or channels between bers ofsaid fibrous material shaping said slurry and removing water from saidshaped slurry until dry to shrink said wet constituents of said shapedslurry to form said intercommunicating pores or channels.

19. The method of making an acoustic tile comprising a mineral wool anda binder and containing a multiplicity of intercommunicating pores orchannels therethrough which comprises making a slurry of precipitatedalkali silicate, and mixing said mineral wool therewith, making anadhesive mixture comprising sodium silicate, mixing said adhesivemixture with said slurry to form a thick slurry, said adhesive being ofsuch composition that on drying it shrinks sufilciently to leave amultiplicity of intercommunicating pores or channels between fibres ofsaid fibrous material shaping said thick slurry and removing water fromsaid shaped thick slurry until dry to shrink said combination of wetmaterials added to said mineral wool to form said intercommunicatingpores and channels.

20. The method of making an acoustic tile comprising a mineral wool anda binder and containing a multiplicity of intercommunicating pores orchannels therethrough, which comprises making a slurry of precipitatedsodium silicate and paper pulp and mixing said mineral wool therewith,mixing alkali silicouoride with sodium silicate to form an adhesivemixture, mixing said adhesive mixture with said slurry to form a thickslurry, said adhesive being of such composition that on drying itshrinks suiliciently to leave a multiplicity of intercommunicating poresor channels between fibers of said brous material shaping said thickslurry and removing water from said shaped thick slurry until dry toshrink said combination of wet materials added to said mineral wool toform said intercommunicating pores and channels.

21. The method of making an acoustic absorber comprising a brousmaterial and a binder and containing a multiplicity ofintercommunicating pores or channels therethrough which comprises mixingsaid brous material with a wet adhesive comprising an alkali silicate toform a thick slurry, said adhesive being of such composition that ondrying it shrinks suirlciently to leave a multiplicity ofintercommunicating pores or channels between bers of said fibrousmaterial brush tamping said slurry into shape, and removing water fromsaid shaped mixture until dry substantially without intumescence of saidsilicate to shrink said wet constituents of said shaped slurry to formsaid intercommunicating pores or channels.

22. The method of making an acoustical absorber comprising an inorganicbrous material and a binder and containing a multiplicity ofintercommunicating pores or channels therethrough which comprises mixingan anti-migrating agent with alkali silicate to form a wet adhesive,mixing said brous material with said 14,0 wet adhesive to form a thickslurry, said adhesive being of such composition that on drying itshrinks sufllciently to leave a multiplicity of intercommunicating poresor channels between bers of said fibrous material shaping said thickslurry, and removing water from said shaped thick slurry until dry byrst subjecting said shaped thick slurry to light pressure and suctionand then subjecting it to an elevated temperature, the temperature beinglow enough to tXamlnei 6 greivent any substantial intmnescence of saidad- 23. As a step in the method of making aporous pad comprising afibrous material and a binder.

the method which-comprises removing the excess liquid contained thereinduring the manufacture thereof from a shaped slurry of said brousmaterial and a wet adhesive by applying both suction and light pressureon opposite surfaces of said shaped slurry, said pressure beingsufficiently light so that it does not appreciably collapse the fibrousframework about the interstices resulting from the removal of the execsliquid from said shaped slurry.

24. The combination of steps in the method of making a porous padcomprising a mineral wool and a binder which comprises making a slurryof said mineral wool and a wet adhesive, forming a pad of said slurry,and applying both suction and light pressure on opposite surfaces Vofsaid slurry, said pressure being suiliciently light so that it does notappreciably collapse the fibrous framework about the intersticesresulting from the removal of the excess liquid from said shaped slurry.

25. In the manufacture of a porous product comprising a mineral wool anda binder, the method for removing water from a slurry of said mineralwool and a wet adhesive during the forming operation which comprisessubjecting one surface of said slurry to a suction and also subjectingthe opposite surface thereof to light air pressure,j said pressure beingsumciently light so that it does not appreciably collapse the flbrousframework about the interstices resulting from the removal of the excessliquid from said shaped slurry MAX H. KLlEFOTH.

